1. Technical Field
The present invention relates to an ink jet recording apparatus and an ink jet recording method.
2. Related Art
As recording apparatuses that can record (print) on a variety of recording media, ink jet recording apparatuses have been known. JP-A-2010-173256 describes, as such an apparatus, a large format printer (LFP) for printing on relatively large recording media. This recording apparatus includes a platen for supporting a recording medium in the recording region, a transporting unit for transporting a recording medium onto the platen, and an ink jet head for discharging an ink on the recording medium and is configured so as to form images, characters, etc. by discharging ink droplets while scanning the ink jet head in a direction crossing the transporting direction of the recording medium.
In general, such an ink jet recording apparatus includes a maintenance unit for maintaining or recovering a satisfactory ink-discharging state. The maintenance unit includes, for example, a capping member for capping the nozzle face of the ink jet head and a wiping member for wiping the nozzle face.
The capping member air-tightly covers the nozzle face during the period when the ink jet recording apparatus is not used (non-operation state) to prevent the ink exposed at the nozzle or adhering to the nozzle periphery from evaporating, and thereby the ink is prevented from thickening and solidifying. The wiping member wipes away the ink adhering to the nozzle face, and thereby clogging of the nozzle by thickening or solidification of the remaining ink can be prevented.
Even in the operation state of the ink jet recording apparatus, the nozzle corresponding to the ink not used (non-discharging nozzle to which any ink-discharging signal for forming an image is not applied) is remained in a non-discharging state, depending on the content of recording. Consequently, clogging of the nozzle by thickening of the ink is apt to occur. In order to recover the nozzle in such a state, flashing (non-recording discharge) is performed. This is performed by intermittently and forcibly discharging an ink onto a recording medium in a region (region outside the scanning range of the ink jet head) other than the discharging region (for recording) to discontinue the non-discharging state and to remove the thickened ink.
However, in an ink jet recording apparatus of larger size and capable of recording more finely, the maintenance unit such as the capping member and the wiping member and the flashing discharge may not prevent nozzle clogging owing to thickening or solidification of an ink during the recording operation.
Specifically, in ink jet recording in recent years, in order to perform recording with higher fineness, the volume of each ink droplet to be discharged must be significantly small, such as several picoliters; the diameter of a nozzle for discharging an ink is reduced; and the energy for discharging ink droplets is also decreased. Because of the small nozzle diameter and the low discharging energy, even if the ink is slightly thickened at the ink jet head, the ink may not be discharged and may cause clogging of the nozzle. In particular, in LFPs compliant to large media, the minimum period of time (interval) to perform the flashing is increased with an increase in the length of the ink jet head to be scanned (scanning distance and scanning time). Accordingly, this tendency (tendency of thickening of ink during the recording operation) is significant in the non-discharging nozzle that does not discharge the ink. As a result, clogging of the nozzle disadvantageously occurs during the recording operation.
As a solution for the above-mentioned problems, for example, the thickened ink is discharged by extremely increasing the potential difference between the driving voltages applied to the piezoelectric elements of the head. However, such a method may increase the volume of the ink droplet or deteriorate the recording quality due to the generation of ink mist.
Thus, the method of preventing clogging by the above-described maintenance unit, flashing, or application of a driving voltage involves a problem that the ink jet recording for recording with higher fineness on a larger medium cannot achieve satisfactory recording.